There is a need for crystal clear block ice for ice carving purposes. To make crystal clear ice, it is necessary that all air be removed from the freezing water, for instance, ordinary ice cubes made in a freezer are full of air and are opaque.
Air may be removed by two methods, stirring and air bubbling. Freezing ice must be continuously stirred. Since a standard three hundred pound block of ice takes about forty-eight hours to freeze, this has to be done by automatic apparatus. A main problem is that ice forms from the bottom of the container upwardly so that the stirring apparatus must be gradually removed so that it will not get frozen in.
The air may also be removed by bubbling air out of the freezing water by forcing air into the bottom of the container. Since ice forms from the bottom, the air tube must be gradually retracted from the botom so that it will not be frozen in.